The increasing power density of vehicle dynamoelectric machines has resulted in some electric machines that use the housing of the machine as a heat sink for electronic components and circuits. Because of the increasing number of electronic components and circuits in modern vehicles, in some situations there may also be a desire to isolate electrical systems in order to reduce disruptive currents and electromagnetic interference (EMI) between components and circuits.
Vehicle alternators produce three-phase alternating current that is rectified into a direct current. The associated voltage can be stored in a battery of a vehicle or be used directly by the electrical circuit of the vehicle, which is supplied with a direct current (DC) voltage. Rectification of the three-phase alternating current is generally obtained by means of a rectifier bridge having six power diodes. Three of these diodes are the positive diodes, and these positive diodes are connected between the phase terminals of the stator windings of the alternator and the positive terminal B+ of the alternator which is connected to the battery and the electrical circuit of the vehicle. Three further diodes, namely the negative diodes, are connected between electrical ground or earth of the vehicle and the aforementioned phase terminals of the stator windings.
The positive and negative diodes make up a rectifier bridge that is subjected to high current. Hence, it is necessary to cool the diodes in the most effective way possible. To this end, the diodes are commonly mounted on metal plates arranged on the outside of the alternator. The metal plates not only serve as mounting plates, but also serve as a heat sink designed to dissipate heat produced by the diodes. The diodes are typically grouped on two carrier plates, one of which is reserved for the positive diodes, and the other for the negative diodes. The rectifier diodes are inserted by pressure in receiving bore holes of the carrier plate/heat sink, or are soldered to the carrier plate using appropriate solder alloys. The end wires connected to the rectifier diodes enable the rectifier diodes to be connected to external sources.
In such an alternator arrangement where the rectifier bridge is mounted on carrier plates, the negative diodes of the system are connected to vehicle ground/battery return path. The vehicle ground/battery return path is often provided by the engine itself, including the alternator housing. However, in some vehicle designs, current flow through the engine can create problems with the engine's electronic control module (ECM) and/or other electronics packages. For example, current through the return path may result in electromagnetic interference (EMI) that disrupts the operation the ECM.
In view of the foregoing, it would be desirable to provide an alternator arrangement where disruptive return path current flows are avoided. It would also be desirable if the size of the alternator remains relatively small in order to avoid overcrowding in the engine compartment.